FIG. 16 shows a laser diode-excited solid laser unit based on a conventional type of power supply unit for laser excitation. A power supply unit 100 for laser excitation outputs a current having a current value set by a current setting device 102 to a laser diode 106 as an exciting unit in synchronism with a reference pulse signal (laser power output signal) outputted from a reference oscillator 104.
The laser diode 106 outputs excitation light by energization and excites a solid laser medium 108 comprising a YAG rod or the like, and the solid laser medium 108 outputs a laser in a pulse form from an optical resonator 116 comprising a total reflection mirror 112 provided in the rear side thereof and a half reflection mirror 114 provided in the front side (output side) thereof.
FIG. 17A to FIG. 17C show a power output waveform and a laser output waveform according to the conventional type of power supply unit shown in FIG. 16. FIG. 17A shows a power output waveform when a current set value PI by the current setting device 102 is low, and FIG. 17B shows a power output waveform when the current set value PI by the current setting device 102 is high respectively, while a reference sign La in FIG. 17C shows a laser output waveform when the current set value PI is low, and a reference sign Lb therein shows a laser output waveform when the current set value PI is high respectively.
A power output waveform in the conventional type of power supply unit for laser excitation is, as shown in FIGS. 17A and 17B, a simple rectangular waveform regardless of amplitude of current set value PI is constant at one pulse.
As the conventional type of power supply unit for laser excitation outputs a current as a pulse with one simple rectangular waveform (constant current set value at one pulse), if the current set value PI is low, laser output becomes as indicated by the reference sign La in FIG. 17C, which shows that the delay Da in rising of the laser output to power output (laser output signal) is larger, so that 50 to 70 .mu.s is required for laser output.
This delay becomes smaller, by making a current set value higher, according to the set value, but even if the value is set to a quite high current value (twice to three times), the delay Db can not be reduced to not more than 20 to 30 .mu.s in the laser output as indicated by the reference sign Lb in FIG. 17C.
Regardless of the current set value, rise times Ta, Tb required for laser output to reach its stable state increase, as shown in FIG. 17C, with a first order lag therebetween and a time of 100 to 200 .mu.s has to be required.
When pulse laser output is used for laser machining, and if a pulse frequency is specified to be 1 kHz and a duty to be 10% as typical machining conditions, a pulse width is 100 .mu.s, which corresponds to a time t in FIG. 17C. Under the machining conditions, when the current set value PI is low, the laser output La can hardly be effected, and even when the current set value PI is high, the laser output Lb in its stable state can not be effected, in which the output waveform is a waveform like a chopping wave. For this reason, if the pulse frequency is set to be high and the duty is set to be low in the conventional type of power supply unit, characteristics in machining such as cutting are degraded.
As described above, the conventional type of power supply unit for laser excitation has had such problems that quick response of laser output can not be made, so that an accurate pulse laser can not be outputted when machining is carried out with short pulses.